Kinetics for Isobaric-Isothermal Inactivation of Bacillus subtilis α-Amylase

Abstract

Isobaric−isothermal inactivation of Bacillus subtilis α-amylase (BSA, 15 mg/mL in Tris-HCl at pH 8.6) in the pressure range 1–750 MPa and the temperature range 25–85 °C could be accurately described by a first-order kinetic model. The kinetic parameters (k, Ea, and Va) were calculated at different pressure and temperature levels. At reference temperature (40 °C) and reference pressure (500 MPa), isobaric−isothermal inactivation was characterized by an Ea value of 74.8 kJ/mol, a Va value of −23.6 cm3/mol, and an inactivation rate constant of 0.0343 min−1. The influence of 15% glycerol on thermal and pressure−temperature stability of BSA was investigated. In both cases, a stabilizing effect of this additive was found, since the kref value was significantly reduced. Furthermore, a pressure−temperature kinetic diagram, indicating the possible synergistic and antagonistic effects of pressure and temperature on the inactivation of BSA, was constructed. Based on this diagram, a model describing the dependence of the inactivation rate constant on pressure and temperature, in the pressure range 250–750 MPa, was formulated.